1. Field of the Invention
This invention relates to pipettors and pipette tips and more particularly to a piston free pipettor and a self-aligning and self-sealing pipette tip.
2. Description of the Related Art
Pipetting systems are used in laboratories for the transfer of relatively small quantities of liquids in a precise and accurate manner. The liquid is normally drawn into the tips by suction and is subsequently released into the wells of microtiter plates or other receptacles. Frequently the transfer involves samples, which are moved from one set of spaced receptacles to another set of receptacles.
The use of pipette devices for the transfer and dispensing of precise quantities of fluids in analytical systems is well known as is the use of disposable tip members for such pipettes. Disposable tips accommodate the serial use of such pipette devices in the transfer of different fluids without carryover or contamination of a second sample from a disposable pipette tip used with a first sample. The first tip is discarded and replaced by a second disposable tip before pipetting the second sample.
Generally speaking, prior disposable pipette tips are formed of a plastic material and are of a hollow, elongated, generally conical shape with an open proximal end for receiving and releasably mating with the distal end of an elongated, generally conical, pipette tip mounting shaft of a pipette device. Ideally, the disposable tip should slide easily onto the mounting shaft to an axial position adjacent a lower end of a tip ejection mechanism of the pipette device. Thus located, the pipette tip should be laterally stable on the shaft, free from external rocking relative to the shaft (as during xe2x80x9ctouching offxe2x80x9d), and should form a fluid tight annular seal with the mounting shaft. Then when it is desired to replace the tip with a new tip, the pipette tip should be easily removed from the mounting shaft by operation of a tip ejection mechanism.
To meet the desired sealing criteria for disposable pipette tips on pipette tip mounting shafts, the inner surface and side walls of the proximal portions of most pipette tips may be axially tapered at a one to one and a half degree greater angle than the distal end of the pipette tip mounting shaft and form an axially elongated frusto-conical annular sealing band. The sealing band may be dimensioned to stretch outwardly (xe2x80x9choop stretchxe2x80x9d) as the distal end of the elongated generally conical pipette tip mounting shaft is forced into the proximal end of the tip to fly seat the tip on the shaft and to create an axially elongated annular fluid tight seal between the sealing band and the mounting shaft. Other pipette tips, may include a plurality of axially-spaced compressible annular sealing rings on an inner surface of the proximal end portion of such tips. The rings create multiple axially spaced fluid tight annular seals between the outer surface of the pipette tip mounting shaft and the inner surface of the proximal end portion of the tip which by virtue of the axially spaced rings is laterally stabilized against undesired rocking on the shaft during touching off.
The design criteria for disposable pipette tips demand that they be stably mountable on and form a fluid tight seal with a pipette mounting shaft is more easily achieved than the design criteria that disposable pipette tips slide easily onto a pipette tip mounting shaft to an axial location forming a fluid tight seal and then be easily removable from the mounting shaft when it is desired to replace the tip.
As previously stated, standard small and moderate volume pipette tips include a frusto-conical annular sealing band or inner surface for engaging and sealing with the tapered distal end of a pipette tip mounting shaft. The angle of taper of the sealing surface usually approximates (e.g., one and one-half degrees greater than) that of the mounting shaft (e.g., two to five degrees). Thinning the side wall of the standard small and moderate volume pipette tips in the region of such a sealing band does little to reduce the mounting and ejection forces required to move such a tip to a sealing location and then eject the pipette tip from the mounting shaft. In forming the desired annular seal, the frusto-conical annular region is required to stretch like a hoop (hoop stretch) outwardly normal to the mating sloping surface of the pipette tip mounting shaft. Large reactive forces in the tip material resist such hoop stretching and require the exertion of large axial forces (e.g., one to three (1-3) or more pounds) on the tip in order to mount the tip on the mounting shaft and create the necessary annular fluid tight seal. Such reactive forces increase as the tip is driven toward the tip ejection mechanism of the associated pipette device.
Due to the foregoing, it can be seen that the efficient mounting of disposable pipette tips by the insertion of a mounting shaft into the pipette tip entails some problems that have yet to be resolved by the art which the present invention addresses.
Disposable pipette tips are commonly mounted and stored in sterilizable racks. Such racks commonly include a support tray having an array of holes for receiving distal ends of pipette tips to vertically orient the pipette tips in a spaced rectilinear pattern with open proximal ends of the tips exposed to receive the mounting shafts of a pipette device onto which the pipette tips are to be mounted. For example, to mount the disposable pipette tips contained in a tip rack on the shafts of a multi-channel pipette, the pipette device is placed over the rack with its several mounting shafts aligned with the open proximal ends of an aligned series of the pipette tips. After a slight initial insertion of the mounting shafts into the open proximal ends of the aligned pipette tips, a relatively large downward force is exerted on the pipette device to drive the mounting shafts into the tip members. The pipette tips are thus very firmly seated on the mounting shafts and are lifted from the rack with upward movement of the multi-channel pipette.
Unfortunately, in practice, such multiple pipette tip mounting procedures often result in some of the pipette tips being mounted at different axial orientations on some of the mounting shafts or mandrels. However, if the pipettor channels are ganged together, the axial orientation would be the same on all tips. However, the force of the seal may vary on each tip due to the variance in internal tip sizes at the places of sealing. In an attempt to eliminate such non-uniform mounting of pipette tips on the several channels of a multi-channel pipette, users often rock the pipette as the mounting shafts are driven by relatively high axial forces into the tips supported by a pipette tip rack to drive the tips toward the lower surface of the tip ejector mechanism of the pipette.
Additionally, the prior pipette tips frequently relied upon the use of O-rings to provide a seal between the pipette tip and the mandrel or manifold into which the pipette tip fit. Several disadvantages arise from the use of O-rings, not the least of which is the greater expense and manufacturing. Additionally, O-rings require lubrication and other activities leading to high maintenance with respect to such O-rings. O-rings need replacement from time to time and due to compression introduce an element of unreliability into the volumes pipetted especially as needed amounts of pipetted liquids become smaller and smaller and progress further and further into the microvolume range.
Consequently, it would be an advance in the art to provide pipette tips that generally do not require a relatively high degree of force or pressure in order to secure them to a mounting shaft or other mounting construction. It would additionally be advantageous to provide such a system to allow a single precise and accurate machine to both aspirate and dispense liquids, as well as to hold the pipette tips in place. This would allow more automated processing of pipetting procedures and allow human attention to be devoted to other more important activities. The present invention provides solutions to these and other problems and disadvantages in the prior art.
The present invention provides an automated pipetting machine that automatically sets and dislodges the pipette tips, as well as providing automatic pipetting operations.
Instead of the usual configuration where a piston moves relative to the pipette tip, a pipette block engages and surrounds the open proximal end of the pipette tips. The pipette tips themselves are held in place with respect to a chassis by a locking plate system. The pipette block then moves vertically with respect to the locking plate system in order to apply or diminish pressure within the pipette tip. This respectively causes the pipette tip to expel/dispense or aspirate fluid at the tip of the pipette. A sliding seal is present between the open proximal end of the pipette tip and the circumscribing surface of the pipette block. By means of a precision motor, precise and accurate amounts of fluid can be dispensed or aspirated by the pipette tips.
Additional motors allow for the automatic locking and unlocking of the locking plate system so that the pipette tips are automatically locked and unlocked into place. Additionally, a third motor disposes the entire pipetting assembly vertically with respect to underlying microtiter plates, other receptacles, and/or pipette tip holders.
The pipettor and pipette tips of the present invention enable precise and accurate amounts of fluid to be pipetted in a piston-less system that is reliable and which lends itself to a high degree of automation.
The present invention also provides pipette tips that require no O-rings in order to provide a reliable seal. For this and other reasons, manufacturing costs are lowered and a more advantageous pipette tip is provided that is reliable and useful in nature.
It is an object of the present invention to provide an automatic pipettor.
It is yet another object of the present invention to provide a pipette tip that may be used in the pipettor of the present invention without conventional O-rings, as well as other pipetting systems whether manual or automated.
It is yet another object of the present invention to provide a relatively low maintenance, multiple-pipette tip pipettor that is free of pistons while delivering precise and accurate amounts of fluids by pipetting.
It is yet another object of the present invention to provide a pipettor that lends itself to automated processes.
It is yet another object of the present invention to provide a disposable pipette tip.
It is yet another object of the present invention to provide a pipette tip that is inexpensive to manufacture.
It is yet another object of the present invention to provide a pipette tip that is usefully implemented in both manual and automated processes.
It is yet another object of the present invention to provide a pipette tip that can be used in plungerless and pistonless pipettors.
It is yet another object of the present invention to provide a pipette tip that provides a seal with the adjacent pipetting mandrel or manifold without the use of O-ring seals.
These and other objects and advantages of the present invention will be apparent from a review of the following specification and accompanying drawings.